Fuel cell system with grid independent operation and DC microgrid capability

ABSTRACT

A fuel cell system includes grid independent operation with DC microgrid capability. This fuel cell system has a capability of operation with and without the grid, and with DC micro-grid capability.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application is a continuation of U.S. application Ser. No.13/295,527, filed Nov. 14, 2011, which claims benefit of U.S.provisional application 61/413,629, filed Nov. 15, 2010, both of whichare incorporated herein by reference in its entirety.

BACKGROUND

Electrical power systems can be used to provide electrical power to onemore loads such as buildings, appliances, lights, tools, airconditioners, heating units, factory equipment and machinery, powerstorage units, computers, security systems, etc. The electricity used topower loads is often received from an electrical grid. However, theelectricity for loads may also be provided through alternative powersources such as fuel cells, solar arrays, wind turbines, thermo-electricdevices, batteries, etc. The alternative power sources can be used inconjunction with the electrical grid, and a plurality of alternativepower sources may be combined in a single electrical power system.Alternative power sources are generally combined after conversion oftheir DC output into an alternating current (AC). As a result,synchronization of alternative power sources is required.

In addition, many alternative power sources use machines such as pumpsand blowers which run off auxiliary power. Motors for these pumps andblowers are typically 3-phase AC motors which may require speed control.If the alternative power source generates a direct current (DC), thedirect current undergoes several states of power conversion prior todelivery to the motor(s). Alternatively, the power to the motors forpumps, blowers, etc. may be provided using the electrical grid, aninverter, and a variable frequency drive. In such a configuration, twostages of power conversion of the inverter are incurred along with twoadditional stages of power conversion for driving components of the ACdriven variable frequency drive. In general, each power conversion stagethat is performed adds cost to the system, adds complexity to thesystem, and lowers the efficiency of the system.

Operating individual distributed generators such as fuel cell generatorsboth with and without a grid reference and in parallel with each otherwithout a grid reference is problematic in that switch-over from currentsource to voltage source must be accommodated. Additionally, parallelcontrol of many grid independent generators can be problematic.

To address the mode mode-switch-over issue, a double-inverterarrangement may be utilized. This allows one inverter to be used in gridtie and a second inverter to be used with the stand-alone load. Anexemplary double-inverter arrangement with a load dedicated inverterthat is located internally in an input/output module of a solid oxidefuel cell (SOFC) system is described in U.S. patent application Ser. No.12/148,488 (filed May 2, 2008 and entitled “Uninterruptible Fuel CellSystem”), the disclosure of which is incorporated herein by reference inits entirety for all purposes.

Another approach is to drop power for 5-10 cycles to switch modes. If asingle inverter is used, a time of 5-10 cycles would be required to dropgrid tie and establish voltage mode control.

Yet another approach is to use frequency droop to control the amount ofpower sharing in grid tied export or in load stand alone output control.

SUMMARY

Embodiments are generally directed to architectures and methods in whichan uninterruptable power module (UPM) comprises a load-dedicatedinverter. The UPM is preferably externally located with respect to theSOFC system power and input/output modules and may be placed adjacent tothe UPM modules of other SOFC systems. These may then be readilycontrolled in parallel with each other with the stand-alone load.

In a first embodiment, a fuel cell system comprises a power modulecomprising at least one fuel cell segment, an input output modulecomprising at least one first inverter, and an uninterruptible powermodule comprising at least one second inverter. The power modulecomprises a first housing, the input output module comprises a secondhousing which is separate from the first housing, and theuninterruptible power module comprises a third housing which is separatefrom the first and the second housings.

In a second embodiment, the at least one fuel cell segment iselectrically connected in parallel to the at least one first inverterand the at least one second inverter, the at least one first inverter iselectrically connected to a load through an electrical grid, and the atleast one second inverter is electrically connected to the load withoutusing the electrical grid.

In a third embodiment of the invention, the output of the SOFC powermodules are paralleled at the DC-output point, and a DC bus is created.This DC bus forms a DC micro grid connecting any number of SOFC systemstogether. The UPM may be a large assembly capable of output of manymultiples of the output of the SOFC systems themselves.

In a fourth embodiment, a fuel cell system is operated with an electricvehicle (EV) charging module (ECM) to charge EV batteries.

Additional alternative embodiments are also described.

DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram illustrating a system according to anembodiment.

FIGS. 1B to 1K illustrate the system of FIG. 1A in various modes ofoperation.

FIGS. 2 and 3 are block diagrams illustrating a DC microgrid accordingto an embodiment.

FIG. 4 is a block diagram illustrating an IOM comprising an inverterthat is configured for “bi-directional” operation according to anembodiment.

FIG. 5 is a block diagram illustrating an IOM comprising an inverterthat is configured for dual mode functionality according to anembodiment.

FIGS. 6A-6E illustrate various modes of operation of the system of thetype shown in FIG. 1A. to provide power to an electric vehicle (EV)charging station according to embodiments.

DETAILED DESCRIPTION

Referring to FIG. 1, a fuel cell system according to an embodimentincludes a UPM 102, an input/output module (IOM) 104 and one or morepower modules 106. The power module 106 comprises a first housing, theIOM 104 comprises a second housing which is separate from the firsthousing, and the uninterruptible power module 102 comprises a thirdhousing which is separate from the first and the second housings. Ifthere is more than one power module 106, for example six to ten modules106, then each power module may comprise its own housing. Each housingmay comprise a cabinet or another type of full or partial enclosure, forexample the cabinet described in U.S. application Ser. No. 12/458,355,filed on Jul. 8, 2009 and incorporated herein by reference in itsentirety. The modules may be arranged in one or more rows or in otherconfigurations.

The UPM 102 includes at least one DC/AC inverter 102A. If desired, anarray of inverters may be used. Any suitable inverter known in the artmay be used. The UPM 102 optionally contains an input rectifier, such asan input diode 102B which connects to the output of a DC bus 112 fromthe power module(s) 106 and to the input of the at least one inverter102A. The UPM also optionally contains a boost PFC rectifier 102C whichconnects to the output the electric grid 114, such as a utility grid,and to the input of the at least one inverter 102A.

The IOM 104 may comprise one or more power conditioning components. Thepower conditioning components may include components for converting DCpower to AC power, such as a DC/AC inverter 104A (e.g., a DC/AC inverterdescribed in U.S. Pat. No. 7,705,490, incorporated herein by referencein its entirety), electrical connectors for AC power output to the grid,circuits for managing electrical transients, a system controller (e.g.,a computer or dedicated control logic device or circuit), etc. The powerconditioning components may be designed to convert DC power from thefuel cell modules to different AC voltages and frequencies. Designs for208V, 60 Hz; 480V, 60 Hz; 415V, 50 Hz and other common voltages andfrequencies may be provided.

Each power module 106 cabinet is configured to house one or more hotboxes. Each hot box contains one or more stacks or columns of fuel cells106A (generally referred to as “segments”), such as one or more stacksor columns of solid oxide fuel cells having a ceramic oxide electrolyteseparated by conductive interconnect plates. Other fuel cell types, suchas PEM, molten carbonate, phosphoric acid, etc. may also be used.

Fuel cells are often combined into units called “stacks” in which thefuel cells are electrically connected in series and separated byelectrically conductive interconnects, such as gas separator plateswhich function as interconnects. A fuel cell stack may containconductive end plates on its ends. A generalization of a fuel cell stackis the so-called fuel cell segment or column, which can contain one ormore fuel cell stacks connected in series (e.g., where the end plate ofone stack is connected electrically to an end plate of the next stack).A fuel cell segment or column may contain electrical leads which outputthe direct current from the segment or column to a power conditioningsystem. A fuel cell system can include one or more fuel cell columns,each of which may contain one or more fuel cell stacks, such as solidoxide fuel cell stacks.

The fuel cell stacks may be internally manifolded for fuel andexternally manifolded for air, where only the fuel inlet and exhaustrisers extend through openings in the fuel cell layers and/or in theinterconnect plates between the fuel cells, as described in U.S. Pat.No. 7,713,649, which is incorporated herein by reference in itsentirety. The fuel cells may have a cross flow (where air and fuel flowroughly perpendicular to each other on opposite sides of the electrolytein each fuel cell), counter flow parallel (where air and fuel flowroughly parallel to each other but in opposite directions on oppositesides of the electrolyte in each fuel cell) or co-flow parallel (whereair and fuel flow roughly parallel to each other in the same directionon opposite sides of the electrolyte in each fuel cell) configuration.

Power modules may also comprise other generators of direct current, suchas solar cell, wind turbine, geothermal or hydroelectric powergenerators.

The segment(s) 106A of fuel cells may be connected to the DC bus, 112such as a split DC bus, by one or more DC/DC converters 106B located inmodule 106. The DC/DC converters 106B may be located in the IOM 104instead of the power module 106.

The power module(s) 106 may also optionally include an energy storagedevice 106C, such as a bank of supercapacitors or batteries. Device 106Cmay also be connected to the DC bus 112 using one or more DC/DCconverters 106D.

The UPM 102 is connected to an input/output module (IOM) 104 via the DCbus 112. The DC bus receives power from power modules 106.

The fuel cell system and the grid 114 are electrically connected to aload 108 using a control logic unit 110. The load may comprise anysuitable load which uses AC power, such as one or more buildings,appliances, lights, tools, air conditioners, heating units, factoryequipment and machinery, power storage units, computers, securitysystems, etc. The control logic unit includes a switch 110A and controllogic 110B, such as a computer, a logic circuit or a dedicatedcontroller device. The switch may be an electrical switch (e.g., aswitching circuit) or an electromechanical switch, such as a relay.

Control logic 110B routes power to the load 108 either from the UPM 102or from the grid 114 using switch 110A. The at least one fuel cellsegment 106A and storage device 106C from module 106 are electricallyconnected in parallel to the at least one first inverter 104A in IOM andto the at least one second inverter 102A in the UPM 102. The at leastone first inverter 104A is electrically connected to the load 108through the electrical grid 114 using switch 110A in the first position.In contrast to the circuit shown in U.S. patent application Ser. No.12/148,488 (filed May 2, 2008 and entitled “Uninterruptible Fuel CellSystem”), the grid 114 in FIG. 1A is directly connected to the load 108through the control logic unit 110 without passing through abidirectional inverter. The at least one second inverter 102A iselectrically connected to the load 108 with the switch 110A in thesecond position without using the electrical grid 114 (i.e., the outputof the fuel cell segment 106A does not have to pass through the grid 114to reach the load 108).

Thus, the control logic 110B selects whether to provide power to theload from the electrical grid 114 (or from the fuel cell segment 106Athrough the grid) or through the at least one second inverter 102A. Thecontrol logic 110B may determine a state of the power modules and selecta source to power the load 108 based on the state of the power modules,as described below.

A second switch 116 controls the electrical connection between the IOM104 and the grid 114. Switch 116 may controlled by the control logic110B or by another system controller.

By way of illustration and not by way of limitation, the system containsthe following electrical paths:

-   -   A path to the load 108 from the AC grid 114.    -   A path from the AC grid 114 through the IOM 104 to storage        elements 106C of power modules 106 (for example, supercapacitors        or batteries).    -   A path from the storage elements 106C of the power modules 106,        over the DC bus 112 to the IOM 104 and the UPM 102 in parallel.        The DC bus delivers DC to the inverter in the UPM 102. The        inverter 102A in the UPM 102 or inverter 104A in IOM 104        delivers AC power to the load 108 depending on the position of        the switch 110A.    -   A path from the power modules 106 (which may include power from        the fuel cell segment(s) 106A and/or the storage elements 106C        of the power modules 106), over the DC bus 112 to the IOM 104        and the UPM 102. The DC bus delivers DC voltage to the inverter        in the UPM 102. The inverter 102A in the UPM 102 delivers AC        power to the load 108. Power in excess of the power required by        the load 108 is delivered to the AC grid through an inverter        104A in the IOM 104. The amount of power that is delivered to        the AC grid 114 will vary according the demands of the load 108.        If the amount of power required by the load 108 exceeds the        power provided by the power modules 106, the additional power        demand may be supplied by the AC grid 114 directly to the load        108 through switch 110A in the first position or to the UPM 102        with the switch 110A in the second position. The grid power is        rectified in rectifier 102C in UPM 102 and provided to the        inverter 102A in the UPM 102 and converted back to AC for        powering the load 108.

FIGS. 1B-1K illustrate various modes of operation of the system shown inFIG. 1A. While the embodiments described below illustrate a load 108which requires 100 kW of power and the fuel cell segment(s) 106A whichoutput 200 kW of power in steady state, these values are provided forillustration only and any other suitable load and power output valuesmay be used.

FIG. 1B illustrates the system operation during the installation of thesystem and/or during a period when the load 108 receives power from thegrid 114. As shown in this figure, the fuel cell segment(s) 106A and theenergy storage device 106C are in the OFF state, the IOM 104 inverter104A and the UPM inverter 102A are both in the OFF state and the secondswitch 116 is open such that there is no electrical communicationbetween the IOM and the grid. The control logic switch 110A is in thefirst position to provide power from the grid 114 to the load 108through the control logic module 110. As shown in the figure, 100 kW ofpower is provided from the grid to the load through the control logicmodule.

FIG. 1C illustrates the system operation during IOM start-up andcharging of the energy storage device (e.g., bank of supercapacitors)106C from the grid 114 while the load 108 receives power from the grid114. As shown in this figure, the fuel cell segment(s) 106A are in theOFF state while the energy storage device 106C is in the ON state. TheIOM 104 bi-directional inverter 104A is in the ON state and the UPMinverter 102A is in the OFF state. The second switch 116 is closed suchthat there is electrical communication between the IOM and the grid toprovide power from the grid 114 to the energy storage device 106Cthrough the IOM 104 inverter 104A and the DC bus 112. The control logicswitch 110A is in the first position to provide power from the grid 114to the load 108 through the control logic module 110. As shown in thefigure, 100 kW of power is provided from the grid to the load throughthe control logic module.

FIG. 1D illustrates the system operation during UPM start-up followingIOM start-up. UPM functions by receiving power from the energy storagedevice 106C. UPM provides the power from the energy storage device 106Cto the load 108. As shown in this figure, the fuel cell segment(s) 106Aare in the OFF state and the energy storage device 106C is in the ONstate. The IOM 104 bi-directional inverter 104A is in the ON state andthe UPM inverter 102A is in the ON state. The second switch 116 isclosed such that there is electrical communication between the IOM andthe grid. The control logic switch 110A is in the second position toprovide power from the UPM 102 to the load 108 through the control logicmodule 110. As shown in the figure, 100 kW of power is provided from thegrid 114 to the load 108 through the rectifier 102C and inverter 102A ofthe UPM 102 and then through the control logic module. Some power mayalso be provided to the load 108 from the energy storage device 106C viathe DC bus 112, UPM 102 and control logic module.

FIG. 1E illustrates the steady state operation of the system. In thismode the fuel cell segment(s) 106A is in the ON state to power the load108. The segment(s) 106A may provide 200 kW of power in a steady statemode (this may be the designed power output or a maximum power output).As shown in this figure, the energy storage device 106C is in the ONstate to act as an emergency backup power source. The IOM 104bi-directional inverter 104A is in the ON state and the UPM inverter102A is in the ON state. The 200 kW power output is split between thegrid 114 and the load 108. The second switch 116 is closed such thatthere is electrical communication between the IOM and the grid toprovide 100 kW of power from the fuel cell segment(s) 106A to the grid.The control logic switch 110A is in the second position to provide theother 100 kW of power from the fuel cell segment(s) 106A in the powermodule 106 through the DC bus passing through IOM 104 and through theinverter 102A of the UPM 102 and then through the control logic module110 to the load 108. Preferably, this 100 kW of power does not passthrough the IOM inverter 104A and/or the grid 114 to reach the load 108.While a 200 kW power output split 50/50 between the grid and the load isdescribed above, different power outputs may be used as needed, such as25 kW to 1000 kW, which may be split 10/90 to 90/10 between the grid andthe load.

FIG. 1F illustrates operation of the system during a relatively steadyload 108 increase from 100 kW to 150 kW (i.e., when the load requiresmore power than prior steady state operation). In this mode, more of thepower output of the fuel cell segment(s) is provided to the load andless of this power output is provided to the grid than in the steadstate mode described above. If desired, 100% of the power output may beprovided to the load and 0% to the grid. The fuel cell segment(s) 106Ais in the ON state to power the load 108. As shown in this figure, theenergy storage device 106C is in the ON state to act as an emergencybackup power source. The IOM 104 bi-directional inverter 104A is in theON state and the UPM inverter 102A is in the ON state. The second switch116 is closed such that there is electrical communication between theIOM and the grid to provide 50 kW of power from the fuel cell segment(s)106A through the IOM inverter 104A to the grid 114. The control logicswitch 110A is in the second position to provide 150 kW of power fromthe fuel cell segment(s) 106A in the power module 106 through the DC buspassing through IOM 104 and through the inverter 102A of the UPM 102 andthen through the control logic module 110 to the load 108. Thus, thepower output of the fuel cell segment(s) 106A is preferably splitbetween the grid and the load in this mode. Preferably, the power doesnot pass through the IOM inverter 104A and/or the grid 114 to reach theload 108.

FIG. 1G illustrates operation of the system during a sudden load 108spike which requires more power than the fuel cell segment(s) 106A cangenerate at that time. For example, the load spike is from 100 kW to 225kW while the segment(s) 106A can only generate 200 kW of power in steadystate or in maximum power mode. The fuel cell segment(s) 106A is in theON state to power the load 108. As shown in this figure, the energystorage device 106C is in the ON state to act as an emergency backuppower source. The IOM 104 bi-directional inverter 104A is in the ONstate and the UPM inverter 102A is in the ON state. The second switch116 is closed such that there is electrical communication between theIOM and the grid. However, no power is provided from fuel cellsegment(s) 106A through the IOM inverter 104A to the grid 114 due to theload spike. The control logic switch 110A is in the second position toprovide power from the fuel cell segment(s) 106A in the power module 106and from the grid 114 through the DC bus passing through IOM 104 andthrough the inverter 102A of the UPM 102 and then through the controllogic module 110 to the load 108. In this mode, the power to the load isprovided from both the fuel cell segment(s) and the grid. As shown, 200kW from the segment(s) 106A is provided through the DC bus 112, diode102B, inverter 102A and switch 110A to the load 108, while 25 kW isprovided from the grid 114 through the rectifier 102B, inverter 102A andswitch 110A to the load 108 to achieve a total 225 kW of power requiredby the load. Preferably, the power from the fuel cell segment(s) doesnot pass through the IOM inverter 104A and/or the grid 114 to reach theload 108.

FIG. 1H illustrates operation of the system during a return to normal orsteady state operation after the sudden load 108 spike. The fuel cellsegment(s) 106A is in the ON state to power the load 108. As shown inthis figure, the energy storage device 106C is in the ON state to act asan emergency backup power source. The IOM 104 bi-directional inverter104A is in the ON state and the UPM inverter 102A is in the ON state.The second switch 116 is closed such that there is electricalcommunication between the IOM and the grid. The control logic switch110A is in the second position to provide power from the fuel cellsegment(s) 106A in the power module 106 through the DC bus passingthrough IOM 104 and through the inverter 102A of the UPM 102 and thenthrough the control logic module 110 to the load 108. In this mode, thefuel cell segment(s) continue to output steady state or maximum power(e.g., 200 kW) which is split between the load and the grid. As shown,200 kW from the segment(s) 106A is provided to the IOM 104. IOM 104provides 100 kW of power from fuel cell segment(s) 106A through the IOMinverter 104A to the grid 114. The DC bus 112 provides the remaining 100kW of power from IOM 104 through diode 102B, inverter 102A and switch110A to the load 108. Preferably, the power does not pass through theIOM inverter 104A and/or the grid 114 to reach the load 108.

FIG. 1I illustrates operation of the system during loss of power fromthe grid 114 (e.g., during a black out). The fuel cell segment(s) 106Ais in the ON state to power the load 108. As shown in this figure, theenergy storage device 106C is in the ON state to absorb power from thefuel cell segment(s) 106A and to the soften the “step” that occursduring the loss of the grid power. The IOM 104 bi-directional inverter104A is in the ON state and the UPM inverter 102A is in the ON state.The second switch 116 is opened such that there is no electricalcommunication between the IOM and the grid. A sensor can sense the lossof grid power and a controller can open the switch 116 in response tothe sensed grid outage. The control logic switch 110A is in the secondposition to provide power from the fuel cell segment(s) 106A in thepower module 106 through the DC bus passing through IOM 104 and throughthe inverter 102A of the UPM 102 and then through the control logicmodule 110 to the load 108. In this mode, out of the 200 kW total poweroutput from the segment(s) 106A, 100 kW is provided to the DC bus 112and 100 kW is provided to the energy storage device 106C to soften thestep. The DC bus 112 provides the 100 kW of power from IOM 104 throughdiode 102B, inverter 102A and switch 110A to the load 108. The poweroutput of the segment(s) 106A is then gradually reduced to 100 kW tomeet the requirements of the load 108.

FIG. 1J illustrates operation of the system during loss of power fromthe grid 114 (e.g., during a black out) and in case of a load transient(e.g., increased demand for power from load 108) while the fuel cellsegment(s) output a reduced amount of power (e.g., 100 kW) which meetsthe steady state requirements of the load. The fuel cell segment(s) 106Ais in the ON state to power the load 108. As shown in this figure, theenergy storage device 106C is in the ON state to provide additionalpower to the load 108. The IOM 104 bi-directional inverter 104A is inthe ON state and the UPM inverter 102A is in the ON state. The secondswitch 116 is opened such that there is no electrical communicationbetween the IOM and the grid. The control logic switch 110A is in thesecond position to provide power from the fuel cell segment(s) 106A andthe energy storage device 106C in the power module 106 through the DCbus passing through IOM 104 and through the inverter 102A of the UPM 102and then through the control logic module 110 to the load 108. In thismode, 100 kW from the segment(s) 106A and 50 kW from the energy storagedevice is provided to the DC bus 112. Thus, the DC bus 112 provides the150 kW of power from IOM 104 through diode 102B, inverter 102A andswitch 110A to the load 108. Preferably, the power does not pass throughthe IOM inverter 104A and/or the grid 114 to reach the load 108.

FIG. 1K illustrates operation of the system during loss of power fromthe grid 114 (e.g., during a black out) and in case of a continuing loadtransient (e.g., continued increased demand for power from load 108).The operation is the same as that shown in FIG. 1J, except that thepower output of the energy storage device 106C is ramped down to zeroover time and the power output of the fuel cell segment(s) is ramped upto the power needed by the load (e.g., 150 kW) over the same time. Thus,over time, the load receives more and more power from the fuel cellsegment(s) 106A and less and less power from the energy storage device106C until all of the required power is supplied to the load 108 by thefuel cell segment(s). Thus, the energy storage device acts as a bridgingpower source during the initial load transient and is then phased outduring the continuing load transient.

Referring to FIGS. 2 and 3, the output of the DC sources 1 to N (210,212 and 214) are paralleled at the DC-output point to one or morerespective DC buses 216, 218, 220. Each DC source 1 to N may compriseone or more power module(s) 106 and an associated IOM 104. The 1 to Nsources feed the customer load via a single UPM 202 assembly. Thus, theplurality of power module/IOM pairs share a common UPM. For example, theDC bus may form a DC micro grid connecting any number of DC sources(e.g., SOFC and power conditioning systems) together at one UPM 202. TheUPM 202 may be a large assembly of individual UPM's 102 shown in FIG. 1Acapable of output of many multiples of the output of the SOFC systemsthemselves. As illustrated, in FIG. 2, the UPM 202 assembly comprises“N” UPMs 102 (i.e., one UPM for each DC source), with a separate DC bus(216, 218 and 220) connecting each DC power source 210, 212 and 214 to adedicated UPM 102. The N UPM's 102 may be arranged in close proximity(e.g., side by side) in one housing or in separate housings to form theUPM assembly 202.

In an alternative embodiment shown in FIG. 3, the assembly 202 ofsmaller dedicated UPM's 102 may be replaced by one large UPM 302. Inthis embodiment, the UPM 302 may include an electrical storage device(e.g., bank of batteries or supercapacitors) and/or a synchronous motor(not illustrated in FIG. 3). In general, UPM inverters may includerotating machinery (e.g., a motor, flywheel, etc.) to enhance storedenergy content and/or increase reliability and inertia of output.

In summary, the DC sources may comprise fuel cell power modules and anIOM. The inverter within each UPM may be a modular assembly of smallerinverters controlled as one large inverter acting with inputs and/oroutputs in parallel. An inverter within the main IOM may be a modularassembly of smaller inverters which are controlled as one large inverteracting with inputs and/or outputs in parallel.

In an embodiment, rectification is provided in the UPM to allow feedfrom the grid when the stacks are off-line, thus providing the load aprotected bus. A boost converter may be used to maintain a good powerfactor to the grid.

In another embodiment, power from stored energy within an SOFC system orthe UPM is used to create a “UPS” unit which has three energy inputs:grid energy; SOFC segment energy; and stored energy (e.g.,ultracapacitors or batteries).

In yet another embodiment, a DC micro-grid is connected to otherdistributed generators such as solar power hardware or wind powerhardware.

In an embodiment, the DC micro-grid is connected to DC loads such as theloads of DC data centers or DC vehicle chargers.

In yet another embodiment, when an IOM and UPM are composed of a clusterof inverters acting in parallel, some or all these inverters may bede-energized depending upon customer load conditions. For example, in a200 kW generation capacity scenario where the customer load is 150 kW,the IOM inverters may be de-energized such that they only support 50 kWinstead of a full 200 kW of grid-tied output. Further, in this scenario,it may be that only a portion of the possible inverters in the IOMassembly may be installed into the IOM, thus providing cost savings interms of equipment required to support the specific customer loadscenario.

Referring to FIG. 4, in an embodiment, an IOM 404 comprises inverters412 that are configured for “bi-directional” operation. Such an invertermay have four-quadrant operation. If the grid-tied inverter has“bi-directional” operation, then the rectified feed does not need to besupplied to the UPM 402. Grid power during start-up may come through thegrid tied inverter 412 instead of via a rectified input to the UPM 402.This embodiment also provides power from power module(s) 406 forprotection of the customer load.

Referring to FIG. 5, in an embodiment, a UPM is not utilized. In thisembodiment, an IOM 504 comprises an inverter 512 that is configured fordual mode functionality. The dual mode inverter 512 is configured tooperate with a grid reference and also in a stand-alone mode, supportinga customer load without a grid reference. In this embodiment an outputpower interruption would be required in order to switch between powergeneration in one mode and another mode.

FIGS. 6A-6D illustrate various modes of operation of the system shown inFIG. 1A in which an electric vehicle (EV) charging module (ECM) is usedinstead of or in addition to the UPM 102. In some modes of operation theECM may perform the functions of the UPM.

The systems of FIGS. 6A-6D offer several advantages when used in EVcharging application. In particular, these systems remove the need forthe grid to supply large peaks of power during quick charging of a largenumber of EVs. The systems can also be used for EV charging in areaswhere it would be too expensive to provide grid power, and where itwould be more cost effective to lay a natural gas pipeline.

Referring to FIG. 6A, an EV charging station comprises one or more powermodules 106, an IOM 104 and an ECM 602. ECM contains a DC/DC converter602A instead of the inverter 102A of UPM 102. In this embodiment, the EVcharging station (e.g., ECM 602) has access to grid power. The EVcharging station may feed power simultaneously to the grid and the EVbattery. A quick (e.g., 10-20 minute) charge may be provided from ECM602 to the EV battery 604 using power from the FCM 106. Whenever an EVbattery 604 is connected to the charging station (e.g., ECM 602) for acharge, the FCM 106 power is automatically diverted from feeding thegrid into the charging station. The diversion of power from the grid tothe EV battery 604 may be accomplished by the control logic asillustrated in FIG. 1A and as discussed previously. The grid power mayserve as a backup power for the charging station when the power modules106 are unavailable.

Referring to FIG. 6B, an EV charging station comprises one or more powermodules 106, an IOM 104, a UPM 102, control logic unit 110 and an ECM602. In this embodiment, the EV charging station 602 may also be used tosupply a customer load 108 while feeding grid power and charging an EVbattery 604. In this configuration, the EV charging station feeds thegrid 114 and also provides uninterrupted power to the customer load 108(such as an office building). The IOM 104 feeds power to the grid 114,while the UPM 102 supplies power to the customer load 108. The ECM 602acts as the EV charging station and draws power from the 400V DC bus112. Thus, the UPM 102 and ECM 602 are connected in parallel to the DCbus 112. While the customer load 108 is supplied without interruption,anytime a vehicle drives in to get charged by the ECM 602, a portion ofthe power being fed to the grid 114 is diverted to the ECM 602 for thetime it takes to charge the EV battery 604. Again, this configurationovercomes the challenge of drawing high peak power from the grid 114,which is a major issue today especially during day time, when the gridis already supplying full capacity.

A typical application of this configuration would be to supply power toan office building. The load 108 from the building (including datacenters, lighting etc) can be supplied clean uninterrupted power fromthe UPM 102, while power is being fed to the grid 114. Charging stationscan be installed at the car park of this building for the employees andvisitors of the company. EV batteries 604 can be charged, and thenparked at the car park. Options for both quick charging (1 C) andtrickle charging (0.1 C) can be provided at the charging stations, basedon the time constraints of the car owner.

Referring to FIG. 6C an EV charging station comprises one or more powermodules 106, a UPM 102, an ECM 602 and a DG set 608. This configurationis suitable for use in remote areas where grid power is not available.In this configuration, the UPM 102 draws power from the DC bus connectedto the power modules 106, and feeds the customer load 108. This customerload 108 also acts like a base load to the power modules 106, whichallows the system to operate at a certain minimum efficiency (in theconfigurations illustrated in FIGS. 6A and 6B above, the grid 114provides the minimum base load for efficient performance). In anembodiment, the power modules 106 and the UPM 102 are rated such thatthe maximum customer load is always supplied while the ECM 602 isoperational. The DG set 608 is used to start up the power modules 106.

Referring to FIG. 6D, an EV charging station comprises one or more powermodules 106 and an ECM 602. This configuration of EV charging stationsis suitable for use where there is no grid power and no customer load isto be supplied. The EV charging station is needed only to act as a powersource for charging the EV battery 604. In this configuration, a batterybank 610 acts as the base load to the EV charging station. This batterybank 610 may be charged using normal charging (0.1 C). An operator of anEV in need of charging the EV battery 604 may obtain a charge from theECM 602. Alternatively, the operator may exchange a discharged EVbattery 604 for one of the batteries in the battery bank 610. The DG 608set is used to start up the power modules 106.

In an embodiment, the EV charging station is configured to takeadvantage of time-of-day pricing and to utilize the storage capacity ofthe EV batteries. For example, the cost of weekday electricity from 11AM to 9 PM may be several times (e.g., 5 times) higher than the cost ofelectricity from 9 PM to 11 AM. In this embodiment, DC power is returnedfrom the EV batteries to the fuel cell system to provide power duringpeak pricing periods and/or to support shortfalls in the power outputfrom the power modules 106 due to an internal power module 106 fault.

Referring to FIG. 6E, the fuel cell system comprises one or more powermodules 106, an IOM 104, a UPM 102, a first control logic unit 110described above, a second control logic unit 702 containing a switch702A and second control logic 702B, and an ECM 602. If desired, thecontrol logic 110B and 702B may be physically combined into a singleunit which performs the functions of the control logic 110B describedabove and functions of control logic 702B described below. In thisembodiment, the power modules 106, IOM 104 and UPM 102 may be used tosupply power to a customer load 108 (e.g., a building, such as an officebuilding) while also being able to provide power to the grid, while theECM 602 may be used for charging an EV battery 604 by drawing power fromthe 400V DC bus 112. Control logic unit 110 performs the functions aspreviously described. Control logic unit 702B performs the functionsdescribed below. Thus, the UPM 102 and ECM 602 are connected in parallelto the DC bus 112.

In an embodiment, the UPM 102 (e.g., the inverter 102A of UMP 102) israted higher than would be required to provide power to load 108 fromthe power modules 106 alone. The additional power handling capabilitiesutilize additional DC power from EV batteries that are connected to theEV charging station (i.e., to ECM 602). The control logic unit 702Bswitches the switch 702A to connect the EV batteries 604 to the ECM 602to receive power from ECM 602, or to DC bus 112 to provide power to theDC bus 112.

By way of illustration and not by way of limitation, the fuel cellsystem contains power module(s) 106 which are capable of delivering afirst value of maximum power (e.g., 200 kW). The UMP 102 is rated toconvert DC to AC to provide a second value of maximum power (e.g., 400kW AC) which is greater than the first value. In other words, theinverter 102A is designed to convert more DC to AC power than the powermodule(s) are capable of providing. The UMP 102 uses the additionalconversion capacity to convert DC power (e.g., up to 200 kW DC) from theEV batteries 604 to AC power to provide to the load 108 or to the grid114.

Thus, DC power from an electric vehicle battery 604 is received at anelectric vehicle charging module (ECM) 602 during a period of higherelectricity price from the grid, the received power is provided to theat least one inverter 102A which converts the received DC power to ACpower, and provides the AC power to a load (e.g., 108 or grid load 114).

In one embodiment, DC power is provided from the at least one fuel cellpower module 106 to the ECM 602, and then provided from the ECM to theelectric vehicle battery 604 when the cost of electricity is lower,prior to the step of receiving DC power.

The combination EV charging station and fuel cell system may be locatedat a business having employees that drive electric cars. Using the timeof day pricing set forth above, these employees would generally parktheir EVs at the business recharging docks and connect the EV batteries604 to the ECM 602 for 8 to 10 hours during the work day. Typically, allthe EV batteries 604 are fully charged (with the switch 702A connectingbatteries 604 to ECM 602) before the price of power from the gridincreases (e.g., by 11 AM) using the power provided from the ECM 602.Then, after the price of the grid power increases (e.g., after 11 AM),logic 702B switches the switch 702A position to connect the EV batteries604 to the DC bus 112. The batteries 604 are then used to provide aportion (e.g., 10-75%, for example 50%) of their stored charge to the DCbus 112. For example, the EV batteries may receive more charge each day(or each week etc.) than they provide back to the DC bus. If desired,the owners of the EVs may not be charged for the net charge theyreceived or be charged a reduced rate compared to the rate for chargingEV batteries from the grid. The charging station could then deliver upto 400 kW AC to load 108 in a peak-shaving load-following manner. Allparties would financially benefit because of the increased price of themid-day electricity.

In another embodiment, the electric vehicle battery is charged at alocation other than the ECM 602 during a lower cost electricity priceperiod prior to the step of receiving DC power from the ECM 602 duringthe higher cost of electricity price period. For example, EVs arecharged at a remote location (e.g., from the grid at home overnight)using lower cost, night time electricity. These EVs may then beconnected to the ECM 602 in the morning. After the price of electricityincreases mid-day (e.g., after 11 AM) the EV batteries 604 deliver apredetermined portion of their stored charge to the DC bus 112. Thus buscan then deliver up to 400 kW AC to load 108 in a peak-shavingload-following manner. The EV owners may be reimbursed for the cost ofprovided power (i.e., for the power they stored at their home anddelivered to the bus 112). Here again all parties financially benefitbecause of the higher price of mid-day electricity.

Of course, the times used in the foregoing examples are for illustrativepurposes only. The charging station may be configured to utilize powerfrom the EV batteries to address the time-of-day pricing for the regionin which the charging station is located.

The above described methods and systems can be readily used withmultiple generators in parallel with a large load, while allowing tightcontrol of frequency and voltage.

The foregoing method descriptions and the process flow diagrams areprovided merely as illustrative examples and are not intended to requireor imply that the steps of the various embodiments must be performed inthe order presented. As will be appreciated by one of skill in the artthe order of steps in the foregoing embodiments may be performed in anyorder. Further, words such as “thereafter,” “then,” “next,” etc. are notintended to limit the order of the steps; these words are simply used toguide the reader through the description of the methods.

One or more block/flow diagrams have been used to describe exemplaryembodiments. The use of block/flow diagrams is not meant to be limitingwith respect to the order of operations performed. The foregoingdescription of exemplary embodiments has been presented for purposes ofillustration and of description. It is not intended to be exhaustive orlimiting with respect to the precise form disclosed, and modificationsand variations are possible in light of the above teachings or may beacquired from practice of the disclosed embodiments. It is intended thatthe scope of the invention be defined by the claims appended hereto andtheir equivalents.

Control elements may be implemented using computing devices (such ascomputer) comprising processors, memory and other components that havebeen programmed with instructions to perform specific functions or maybe implemented in processors designed to perform the specifiedfunctions. A processor may be any programmable microprocessor,microcomputer or multiple processor chip or chips that can be configuredby software instructions (applications) to perform a variety offunctions, including the functions of the various embodiments describedherein. In some computing devices, multiple processors may be provided.Typically, software applications may be stored in the internal memorybefore they are accessed and loaded into the processor. In somecomputing devices, the processor may include internal memory sufficientto store the application software instructions.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentinvention.

The hardware used to implement the various illustrative logics, logicalblocks, modules, and circuits described in connection with the aspectsdisclosed herein may be implemented or performed with a general purposeprocessor, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA) orother programmable logic device, discrete gate or transistor logic,discrete hardware components, or any combination thereof designed toperform the functions described herein. A general-purpose processor maybe a microprocessor, but, in the alternative, the processor may be anyconventional processor, controller, microcontroller, or state machine. Aprocessor may also be implemented as a combination of computing devices,e.g., a combination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration. Alternatively, some blocks ormethods may be performed by circuitry that is specific to a givenfunction.

The preceding description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the describedembodiment. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thescope of the disclosure. Thus, the present invention is not intended tobe limited to the embodiments shown herein but is to be accorded thewidest scope consistent with the following claims and the principles andnovel features disclosed herein.

What is claimed is:
 1. A fuel cell system, comprising: a plurality ofpower modules each comprising at least one fuel cell segment; an inputoutput module comprising at least one first inverter; a plurality ofsecond inverters; at least one uninterruptible power module comprisingat least one of the plurality of second inverters; and a control logicunit comprising a selective connection mechanism; wherein: the at leastone fuel cell segment of each of the plurality of power modules iselectrically connected in parallel to the at least one first inverterand at least one of the plurality of second inverters; the at least onefirst inverter is electrically connected to a load through an electricalgrid, wherein the at least one first inverter is selectivelyelectrically connected to the electrical grid through a switch; theplurality of second inverters are electrically connected in parallel tothe load without using the electrical grid; and the control logic unitis configured to selectively electrically connect the electrical grid tothe load via configuring the selective connection mechanism into a firstposition, to selectively electrically connect the plurality of secondinverters to the load via configuring the selective connection mechanisminto a second position, and to control the plurality of second invertersas a single inverter.
 2. The system of claim 1, wherein the power modulecomprises a first housing, the input output module comprises a secondhousing which is separate from the first housing, and the at least oneuninterruptible power module comprises a third housing which is separatefrom the first and the second housings.
 3. The system of claim 2,wherein the third housing is located adjacent to the load and the firstand the second housings are located further from the load than the thirdhousing.
 4. The system of claim 1, wherein the selective connectionmechanism comprises a switch which is configured to: (i) electricallyconnect the electrical grid to the load and to disconnect the pluralityof second inverters from the load in the first position, and (ii)electrically connect the plurality of second inverters to the load andto disconnect the electrical grid from the load in the second position.5. The system of claim 4, wherein the switch comprises an electricalswitch.
 6. The system of claim 5, wherein the electrical switchcomprises a switching circuit.
 7. The system of claim 4, wherein theswitch comprises an electromechanical switch.
 8. The system of claim 7,wherein the electromechanical switch comprises a relay.
 9. A fuel cellsystem, comprising: a plurality of power modules each comprising atleast one fuel cell segment; an input output module comprising at leastone first inverter and configured for selective connection to anelectrical grid through a switch; a plurality of second inverters,wherein the at least one fuel cell segment of each of the plurality ofpower modules is electrically connected in parallel to at least one ofthe plurality of second inverters; at least one uninterruptible powermodule comprising at least one of the plurality of second inverters; anda control logic unit comprising a selective connection mechanism,wherein the control logic unit is configured to selectively electricallyconnect the electrical grid to a load via configuring the selectiveconnection mechanism into a first position, to selectively electricallyconnect the plurality of second inverters to the load in parallel viaconfiguring the selective connection mechanism into a second position,and to control the plurality of second inverters as a single inverter;wherein the power module comprises a first housing, the input outputmodule comprises a second housing which is separate from the firsthousing, and the at least one uninterruptible power module comprises athird housing which is separate from the first and the second housings.10. The system of claim 9, wherein the third housing is located adjacentto the load and the first and the second housings are located furtherfrom the load than the third housing.
 11. The system of claim 9, whereinthe selective connection mechanism comprises a switch which isconfigured to: (i) electrically connect the electrical grid to the loadand to disconnect the plurality of second inverters from the load in thefirst position, and (ii) electrically connect the plurality of secondinverters to the load and to disconnect the electrical grid from theload in the second position.
 12. The system of claim 11, wherein theswitch comprises an electrical switch.
 13. The system of claim 12,wherein the electrical switch comprises a switching circuit.
 14. Thesystem of claim 11, wherein the switch comprises an electromechanicalswitch.
 15. The system of claim 14, wherein the electromechanical switchcomprises a relay.